Avocado Fruits
Etymology
The word 'avocado' comes from the Nahuatl word ahuacatl ('testicle', a reference to the shape of the fruit). Avocados were known by the Aztecs as 'the fertility fruit'. In some countries of South America such as Argentina, Bolivia, Chile, Peru, and Uruguay the avocado is known by its Quechua name, palta. In other Spanish-speaking countries it is called aguacate, and in Portuguese it is abacate. The fruit is sometimes called an avocado pear or alligator pear (due to its shape and the rough green skin of some cultivars). The Nahuatl ahuacatl can be compounded with other words, as in ahuacamolli, meaning 'avocado soup or sauce', from which the Mexican Spanish word guacamole derives.
Also in some South American countries, the avocado is called "la manzana del invierno". This translates to "the apple of the winter".
Cultivation
The tree grows to 20 m (69 ft), with alternately arranged leaves 12 centimetres (4.7 in) – 25 centimetres (9.8 in) long. The flowers are inconspicuous, greenish-yellow, 5 millimetres (0.2 in) – 10 millimetres (0.4 in) wide. The pear-shaped fruit is 7 centimetres (2.8 in) – 20 centimetres (7.9 in) long, weighs between 100 grams (3.5 oz) – 1,000 grams (35 oz) grams, and has a large central seed, 5 centimetres (2.0 in) – 6.4 centimetres (2.5 in) long.
The subtropical species needs a climate without frost and with little wind. High winds reduce the humidity, dehydrate the flowers, and affect pollination. In particular, the West Indian type requires humidity and a tropical climate which is important for flowering. When even a mild frost occurs, premature fruit drop may occur, although the Hass cultivar can tolerate temperatures down to -1°C. The trees also need well-aerated soils, ideally more than 1 m deep. Yield is reduced when the irrigation water is highly saline. These soil and climate conditions are available only in a few areas of the world, particularly in southern Spain, the Levant, South Africa, Peru, parts of central and northern Chile, Vietnam, Indonesia, parts of southern India, Sri Lanka, Australia, New Zealand, the Philippines, Malaysia, Central America, the Caribbean, Mexico, California, Arizona, New Mexico, Texas, and Florida. Each region has different types of cultivars. Mexico, the center of origin and diversity of this species, is the largest producer of the Hass variety, with over 1 million tonnes produced annually.
Harvest and post-harvest
An average avocado tree produces about 120 avocados annually. Commercial orchards produce an average of 7 tonnes per hectare each year, with some orchards achieving 20 tonnes per hectare.[9] Biennial bearing can be a problem, with heavy crops in one year being followed by poor yields the next. The avocado tree does not tolerate freezing temperatures, and can be grown only in subtropical or tropical climates.
The avocado is a climacteric fruit (the banana is another), which means that it matures on the tree but ripens off the tree. Avocados used in commerce are picked hard and green and kept in coolers at 38 to 42°F (3.3 to 5.6°C) until they reach their final destination. Avocados must be mature to ripen properly. Avocados that fall off the tree ripen on the ground, and depending on the amount of oil they contain, their taste and texture may vary greatly. Generally, the fruit is picked once it reaches maturity; Mexican growers pick Hass-variety avocados when they have more than 23% dry matter and other producing countries have similar standards. Once picked, avocados ripen in a few days at room temperature (faster if stored with other fruits such as apples or bananas, because of the influence of ethylene gas). Premium supermarkets sell pre-ripened avocados treated with synthetic ethylene to hasten the ripening process.[10] In some cases, avocados can be left on the tree for several months, which is an advantage to commercial growers who seek the greatest return for their crop; if the fruit remains unpicked for too long, however, it will fall to the ground.
[edit] BreedingThe species is only partially able to self-pollinate, because of dichogamy in its flowering. This limitation, added to the long juvenile period, makes the species difficult to breed. Most cultivars are propagated via grafting, having originated from random seedling plants or minor mutations derived from cultivars. Modern breeding programs tend to use isolation plots where the chances of cross-pollination are reduced. That is the case for programs at the University of California, Riverside, as well as the Volcani Centre and the Instituto de Investigaciones Agropecuarias in Chile.
The avocado is unusual in that the timing of the male and female flower phases differs among cultivars. There are two flowering types, "A" and "B". "A" cultivar flowers open as female on the morning of the first day and close in late morning or early afternoon. Then they open as male in the afternoon of the second day. "B" varieties open as female on the afternoon of the first day, close in late afternoon and reopen as male the following morning.
"A" cultivars: Hass, Gwen, Lamb Hass, Pinkerton, Reed. "B" cultivars: Fuerte, Sharwil, Zutano, Bacon, Ettinger, Sir Prize, Walter Hole. Certain cultivars, such as the Hass, have a tendency to bear well only in alternate years. After a season with a low yield, due to factors such as cold (which the avocado does not tolerate well), the trees tend to produce abundantly the next season. This heavy crop depletes stored carbohydrates, resulting in a reduced yield the following season, and thus the alternate bearing pattern becomes established.
Propagation and rootstocksWhile an avocado propagated by seed can bear fruit, it takes roughly 4–6 years to do so, and the offspring is unlikely to resemble the parent cultivar in fruit quality. Thus, commercial orchards are planted using grafted trees and rootstocks. Rootstocks are propagated by seed (seedling rootstocks) and also layering (clonal rootstocks). After about a year of growing in a greenhouse, the young plants are ready to be grafted. Terminal and lateral grafting is normally used. The scion cultivar will then grow for another 6–12 months before the tree is ready to be sold. Clonal rootstocks have been selected for specific soil and disease conditions, such as poor soil aeration or resistance to the soil-borne disease caused by phytophthora
DiseasesAvocado trees are vulnerable to bacterial, viral, fungal and nutritional diseases (excesses and deficiencies of key minerals). Disease can affect all parts of the plant, causing spotting, rotting, cankers, pitting and discoloration
A Cultivars
HassWhile dozens of cultivars are grown in California, the Hass avocado is today the most common. It produces fruit year-round and accounts for the majority of cultivated avocados in the US. All Hass avocado trees are descended from a single "mother tree" that was raised by a mail carrier named Rudolph Hass, of La Habra Heights, California. Hass patented the productive tree in 1935. The "mother tree", of uncertain subspecies, died of root rot and was cut down in September, 2002. Medium sized (150-250g) ovate fruit with a black pebbled skin. Nutty rich flavour. Oil 19%. The skin ripens black. A hybrid Guatemalan type, to 26°F. Tree size - 6m x 4m
GwenSeedling bred from Hass x Thille in 1982. Higher yielding and more dwarfing than `Hass' in California. Fruit has an oval shape, slightly smaller than `Hass' (100-200g). Rich, nutty flavour. Skin texture is more finely pebbled than `Hass', dull green when ripe. Not hardy, to 30°F.
PinkertonFirst grown on the Pinkerton Ranch in Saticoy, California, in the early 1970s. Seedling of Hass' Rincon. Large fruit, small seed, green skin deepens in colour as it ripens. The thick flesh has a smooth-texture, creamy, pale green, good flavour and high oil content. It shows some cold tolerance and bears consistently heavy crops. Excellent peeling characteristics. A hybrid Guatemalan type, to 30°F. An important variety in Israel.
ReedDeveloped from a chance seedling found in 1948 by James S. Reed in California. Large round green fruit with a smooth dark, thick glossy skin. Smooth and delicate, slightly nutty flavour. The skin ripens green. A Guatemalan type, to 30°F. Tree size - 5m x 4m.
B Cultivars
BaconDeveloped by a farmer named James Bacon in 1954. Medium-sized fruit. Light taste, smooth green skin. Yellow-green flesh. When ripe, skin remains green but darkens slightly, and fruit yields to gentle pressure. Cold-hardy variety, down to -5°C.
EttingerA Mexican Guatemalan cross, seedling of Fuerte. Originated in Israel and put into production there in 1947. Cold tolerance 4 hours of -6°C in a mature tree. Smooth thin green skin that does not peel easily. The flesh is very pale green.
FuerteA Mexican Guatemalan cross originating in the Mexican state of Puebla. The fuerte earned its name, which means strong in Spanish, after it withstood a severe frost in California in 1913. Hardy to 26°F. Medium-sized pear-shaped fruit with a green leathery skin, easy to peel. Creamy flesh of mild and rich flavour. Oil 18%. The skin ripens green. Tree size - 6m x 4m.
SharwilPredominantly Guatemalan with some Mexican race genes, selected in 1951 by Sir Frank Sharpe at Redland Bay, southern QLD, Australia. The name 'sharwil' is an amalgamation of Sharp and Wilson (J.C. Wilson being the first propagator). Scions were sent from Australia to Hawaii in 1966. A medium-sized fruit with rough green skin closely resembling the Fuerte but slightly more oval in shape. The fruit has greenish-yellow flesh; a rich, nutty flavour; good oil content (20-24%); and small seed. Green skin when ripe. It represents more than 57% of the commercial acreage in Hawaii, and represents up to 20% of all avocados grown in NSW, Australia. It is a regular and moderate bearer with excellent quality fruit. Sensitive to frost. More disease and pest resistant than Fuerte.
ZutanoOrigin R.L. Ruitt, Fallbrook, 1926. Mexican variety, hardy to 25°F. Large pear-shaped fruit. Shiny, thin yellow-green skin. Flesh is pale green with fibers and has a light flavour. Moderate peel ease.
Other cultivarsOther avocado cultivars include Spinks. The fruit of the cultivar Florida, grown mostly outside California, is larger and rounder, with a smooth, medium-green skin, and a less-fatty, firmer and fibrous flesh. These are occasionally marketed as low-calorie avocados. Historically attested varieties (which may or may not survive among horticulturalists) include the Challenge, Dickinson, Kist, Queen, Rey, Royal, Sharpless, and Taft.
Avocado-related international trade issuesAfter the North American Free Trade Agreement (NAFTA) went into effect in 1994, Mexico tried exporting avocados to the US. The US government resisted, claiming that the trade would introduce fruit flies that would destroy California's crops. The Mexican government responded by inviting US Department of Agriculture inspectors to Mexico, but the U.S. government declined, claiming fruit-fly inspection is not feasible. The Mexican government then proposed to sell avocados only to the northeastern US in the winter (fruit flies cannot withstand extreme cold). The US government balked, but gave in when the Mexican government started throwing up barriers to US corn.
Legitimate pest-invasion issues exist, as avocado pests originating in Mexico have made their way to California, including the persea mite and avocado thrips. These pests have increased pest control costs and made previously-relied-upon biological control less feasible. Other potentially disastrous pests, including a weevil, remain risks. Another argument is that the lower prices generated by Mexican (and Chilean) imports would increase the popularity of avocados outside of California, thereby assuaging the loss of profits due to the new competition.
Today avocados from Mexico are allowed in all 50 states. This is because USDA inspectors in Michoacán (the Mexican state where 90% of Hass avocados from Mexico are grown), have cut open and inspected millions of fruit in Uruapan, finding no problems. Imports from Mexico in the 2005–2006 season exceeded 130,000 tonnes.
In 2009, Peru joins Chile and Mexico as an exporter of avocados to the US.
Avocados were more expensive in the US than in most other countries, because those consumed in the US were grown almost exclusively in California and Florida.[clarification needed] The avocado tree requires frequent, deep watering to bear optimal amounts of fruit, particularly in spring, summer, and fall; and due to the increased costs for water in Southern California versus those of prior decades, it is now a costly crop to grow. California produces about 90% of the United States' avocado crop.
Internationally, avocado exports are dominated by Mexico.
Health benefitsHigh avocado intake has been shown to have an effect on blood serum cholesterol levels. Specifically, after a seven-day diet rich in avocados, hypercholesterolemia patients showed a 17% decrease in total serum cholesterol levels. These subjects also showed a 22% decrease in both LDL (bad cholesterol) and triglyceride levels and 11% increase in HDL (good cholesterol) levels.[20] Additionally a Japanese team synthesised the four chiral components and identified
Uses
The fruit of horticultural cultivars ranges from more or less round to egg- or pear-shaped, typically the size of a temperate-zone pear or larger, on the outside bright green to green-brown (or almost black) in color. The fruit has a markedly higher fat content than most other fruit, mostly monounsaturated fat, and as such serves as an important staple in the diet of various groups where access to other fatty foods (high-fat meats and fish, dairy, etc) is limited. A ripe avocado will yield to a gentle pressure when held in the palm of the hand and squeezed. The flesh is typically greenish yellow to golden yellow when ripe. The flesh is prone to enzymatic browning and turns brown quickly after exposure to air. To prevent this, lime or lemon juice can be added to avocados after they are peeled.
The avocado is very popular in vegetarian cuisine, making an excellent substitute for meats in sandwiches and salads because of its high fat content. The fruit is not sweet but fatty, distinctly yet subtly flavored, and of smooth, almost creamy texture. It is used as the base for the Mexican dip known as guacamole, as well as a filling for several kinds of sushi, including California rolls. Avocado is popular in chicken dishes and as a spread on toast, served with salt and pepper. In Brazil, Indonesia, Vietnam, and south India (especially the coastal Karnataka region), avocados are frequently used for milk-shakes and occasionally added to ice cream and other desserts. In Brazil, Vietnam, the Philippines, and Indonesia, a dessert drink is made with sugar, milk or water, and pureed avocado. Chocolate syrup is sometimes added. In Australia and New Zealand, it is commonly served in sandwiches, on toast, or often with chicken. In Ghana, it's often eaten alone in sliced bread as a sandwich.In Sri Lanka it is a popular dessert once well ripened, flesh is thoroughly mashed with sugar/sugar and milk or treacle (a syrup made from the nectar of a particular palm flower).
In Mexico and Central America avocados are served mixed with white rice, in soups, salads, or on the side of chicken and meat. In Peru avocados are consumed with tequeños as mayonnaise, served as a side dish with parrillas, used in salads and sandwiches, or as a whole dish when filled with tuna, shrimps, or chicken. In Chile it is used as a puree in chicken, hamburgers, and hot dogs; and in slices for celery or lettuce salads. The Chilean version of Caesar salad contains large slices of mature avocado. In Kenya, the avocado is often eaten as a fruit, and is eaten alone, or mixed with other fruits in a fruit salad, or as part of a vegetable salad. In Iran it is used as a rejuvenating facial cream.
A puree of the fruit was used to thicken and flavour the liquer Advocaat in its original recipe, made by the Dutch population of Suriname and Recife, with the name deriving from the same source.
